Cats with genetic Gm2 gangliosidosis will be used to develop enzyme replacement methodologies applicable to the treatment of human lysosomal storage diseases associated with mental retardation. Depression of glycosyl-mediated hepatic clearance and enhancement of charge-dependent cellular uptake of human placental Beta-hexosaminidase will be obtained by modifying its carbohydrate chain composition and its net charge. The cellular distribution of native and modified enzymes in visceral organs will be compared using immunofluorescence microscopy. The catabolic activity of the enzymes will be studied in vitro and in vivo. Reversible blood brain barrier permeability will be obtained by controlled cerebral gas embolism and by hyperosmotic infusions. Delivery of native and modified enzymes to the CNS parenchyma, and their uptake by neural cells will be studied in both cases by immunofluorescence microscopy. Neuronal uptake and catabolic effects of native and modified placental enzyme and of Beta-hexosaminidase from plasma and cell culture fluids will be studied in short-term cultures of isolated cortical neurons. These cells will also be used to study selected aspects of ganglioside metabolism. The appropriate combination of methodologies will be applied in affected kittens; the effects on ganglioside storage, aberrant neuronal morphology, and clinical neurologic manifestations will be assessed.